Electrochemical Corrosion Behavior of HiPIMS-Deposited Diamond-like Carbon (DLC) Coatings on AISI 52100 Steel in Synthetic Seawater

This manuscript evaluates the electrochemical corrosion resistance of diamond-like carbon (DLC) coatings deposited via High-Power Impulse Magnetron Sputtering (HiPIMS) on AISI 52100 steel in synthetic seawater. While AISI 52100 steel is valued for its hardness, it is highly susceptible to localized and uniform corrosion in chloride-rich marine environments. In this study, samples were characterized using Raman spectroscopy to analyze sp2/sp3 bonding, and their corrosion behavior was assessed through potentiodynamic polarization, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) over 24 h of immersion. Results demonstrated that the DLC coatings significantly enhanced electrochemical stability, shifting corrosion potentials toward more noble values and reducing the corrosion current density from (1.81 ± 0.12) × 10−7 to (1.03 ± 0.09) × 10−9 mA·cm−2. EIS data revealed high polarization resistance and effective barrier properties, despite a calculated total porosity of 3.06% resulting from intrinsic micro-defects. Although localized subsurface degradation and minor flaking were observed at defect sites, the HiPIMS-deposited DLC coatings effectively mitigated the corrosive impact of synthetic seawater, providing a significant contribution to the electrochemical barrier despite the persistence of electrolyte accessibility mediated by localized defects.